TamTam roundup.

On May 20, 2007, at 2:01 AM, Hal Murray wrote:
>>> Yes, NTP is one of the services provided by the school servers.
>> Ideally, a laptop's NTP server would be determined by a protocol
>> similar to the one used for internet portal and DNS server ---
>> identifying the "closest" server in the mesh. In any case, network
>> propagation time is taken into account by the NTP (although I believe
>> Hal is far more knowledgable than I in such matters...)
>> I'm pretty sure there us a slot allocated in DHCP to specify NTP
> servers.
> That requires some script to get the DHCP info and then rewrite
> ntp.conf.
>> I don't know much about that area. It's not as common as it should
> be,
> mostly because ISPs have their head in the sand about providing NTP
> services
> for their customers which is partly a chicken/egg tangle.
>> One obvious alternative for olpc is to have a magic DNS name that
> resolves to
> the local NTP server.
Maigc DNS names at your service. And since the DNS server used by a
laptop in a school setting will also be the closest mesh portal, the
NTP server can be the closest on the mesh.
> How do the backup scripts find their local server? If they use a
> magic name,
> ntpd should be able to do something similar.
>> ntpd assumes that the network delays between client and server are
> symmetric.
> It fudges the response by half the round trip delay and then
> filters that.
> That works pretty well except for several cases which may not be
> uncommon:
> If you have an asymmetric link like ADSL, you will be off by the
> bandwidth
> differences multiplied by the packet size, even if the link is
> unloaded.
> That gives you a constant offset which is often OK.
>> The filter gets confused by queuing delays if you have a link with
> asymmetric
> loads for extended periods of time, like when downloading a CD over
> SDSL.
>>>> Anybody on the XO side know if NTP is part of the build yet ?
>> I think it is included in 406. The config file is setup to use
> several pool
> servers. That's typical. It's a lot better than nothing but
> generally picks
> servers at random from a set scattered around the world. What you
> really
> want is sane nearby servers where nearby means low network delays
> rather than
> few miles/kilometers.
>> We'll know a lot more when somebody gets some ping data on a
> typical mesh.
> (I realize that "typical" probably doesn't exist, but we have to start
> somewhere.)
>> [I've been using my own ntpd setup in order to collect some
> statistics. I
> noticed the default setup after updating to 406 before I smashed it
> with my
> stuff. I didn't investigate.]